The application of fabric to rectangular panel frames has become more important with the tremendous increase in the use of moveable partitions that define work areas. For decorative and sound-absorbing purposes, the usual panel structure is a rectangular frame of metal or wood, with a fabric stretched rather tightly over it. The fabric may be on one or both sides of the frame; and in the latter case, insulating material may be interposed. The fabric should be just tight enough so that it is not easily pinched together manually to form a ridge. Excessive or unbalanced stretching distorts the fabric, and this is not satisfactory at all with printed materials. Fabrics typically stretch with different modluli of elasticity along the length than they do across the width of the fabric roll. Equal tension in both directions thus induces greater extension in one direction than it does in the other. The usual rectangular panel also obviously will have greater fabric extension along the longer dimension, for equal application of force.
Various types of tightening devices have been developed for screen frames and similar units. These have typically involved sets of opposed jaws that grip the fabric, and then are moved laterally outward from the central area to produce the required tension in the fabric over the panel frame, followed by securing the fabric to the panel frame with staples or other fastening means. The Timphony U.S. Pat. No. 4,317,301 discusses a device that pulls the fabric around the edges of the panel frame, and toward the central area along the underside of the frame. The fabric is thus continuous along the top, edge, and bottom of the panel frame, and is stapled along any of these surfaces. Obviously, the amount of fabric required in this arrangement is a significant cost factor, and the interference of the jaws at the corners as they move inward can be a problem, if tension is to be applied along adjacent sides at the same time.